MIB–MIP is a mycoplasma system that captures and cleaves immunoglobulin G Yonathan Arfia,b,1, Laetitia Minderc,d, Carmelo Di Primoe,f,g, Aline Le Royh,i,j, Christine Ebelh,i,j, Laurent Coquetk, Stephane Claveroll, Sanjay Vasheem, Joerg Joresn,o, Alain Blancharda,b, and Pascal Sirand-Pugneta,b aINRA (Institut National de la Recherche Agronomique), UMR 1332 Biologie du Fruit et Pathologie, F-33882 Villenave d’Ornon, France; bUniversity of Bordeaux, UMR 1332 Biologie du Fruit et Pathologie, F-33882 Villenave d’Ornon, France; cInstitut Européen de Chimie et Biologie, UMS 3033, University of Bordeaux, 33607 Pessac, France; dInstitut Bergonié, SIRIC BRIO, 33076 Bordeaux, France; eINSERM U1212, ARN Regulation Naturelle et Artificielle, 33607 Pessac, France; fCNRS UMR 5320, ARN Regulation Naturelle et Artificielle, 33607 Pessac, France; gInstitut Européen de Chimie et Biologie, University of Bordeaux, 33607 Pessac, France; hInstitut de Biologie Structurale, University of Grenoble Alpes, F-38044 Grenoble, France; iCNRS, Institut de Biologie Structurale, F-38044 Grenoble, France; jCEA, Institut de Biologie Structurale, F-38044 Grenoble, France; kCNRS UMR 6270, Plateforme PISSARO, Institute for Research and Innovation in Biomedicine - Normandie Rouen, Normandie Université, F-76821 Mont-Saint-Aignan, France; lProteome Platform, Functional Genomic Center of Bordeaux, University of Bordeaux, F-33076 Bordeaux Cedex, France; mJ. Craig Venter Institute, Rockville, MD 20850; nInternational Livestock Research Institute, 00100 Nairobi, Kenya; and oInstitute of Veterinary Bacteriology, University of Bern, CH-3001 Bern, Switzerland Edited by Roy Curtiss III, University of Florida, Gainesville, FL, and approved March 30, 2016 (received for review January 12, 2016) Mycoplasmas are “minimal” bacteria able to infect humans, wildlife, introduced into naive herds (8). In goats and sheep, mycoplasma and a large number of economically important livestock species. My- infections are predominantly caused by Mycoplasma capricolum coplasma infections include a spectrum of clinical manifestations subsp. capricolum, Mycoplasma capricolum subsp. capripneumoniae, ranging from simple fever to fulminant inflammatory diseases with and Mycoplasma mycoides subsp. capri. These pathogens cause acute high mortality rates. These infections are mostly chronic, suggesting to peracute diseases, often lethal, including contagious caprine that mycoplasmas have developed means to evade the host immune pleuropneumonia (9). Mycoplasmas also infect swine (Mycoplasma response. Here we present and functionally characterize a two-pro- tein system from Mycoplasma mycoides subspecies capri that is in- hyopneumoniae, Mycoplasma hyorhinis) (10) and economically im- volved in the capture and cleavage of IgG. The first component, portant Galliformes, such as chicken and turkey (Mycoplasma galli- Mycoplasma Ig binding protein (MIB), is an 83-kDa protein that is able septicum, Mycoplasma synoviae,andMycoplasma iowae)(11). to tightly bind to the Fv region of a wide range of IgG. The second Overall, the genetic bases of mycoplasma pathogenicity remain component, Mycoplasma Ig protease (MIP), is a 97-kDa serine prote- unclear, but they appear to lack the effectors exported through ase that is able to cleave off the VH domain of IgG. We demonstrate specialized secretion systems found in numerous bacterial pathogens that MIB is necessary for the proteolytic activity of MIP. Cleavage of (12). In addition, the number of toxins or other toxic compounds IgG requires a sequential interaction of the different partners of the produced by mycoplasmas is limited. Among the known exceptions is system: first MIB captures the IgG, and then MIP is recruited to the the capacity of several mycoplasmas to produce hydrogen peroxide MIB–IgG complex, enabling protease activity. MIB and MIP are (H2O2) as a by-product of glycerol metabolism (13, 14). For a small encoded by two genes organized in tandem, with homologs number of Mycoplasma species, the secretion of virulence-mediating found in the majority of pathogenic mycoplasmas and often in My- multiple copies. Phylogenetic studies suggest that genes encod- proteins was demonstrated. For instance, the rodent pathogen ing the MIB–MIP system are specific to mycoplasmas and have coplasma arthritidis secretes the effector Mycoplasma arthritidis mi- been disseminated by horizontal gene transfer. These results togen, an immunomodulatory protein that demonstrates classical highlight an original and complex system targeting the host im- superantigenic properties, resulting in an excessive activation of munoglobulins, playing a potentially key role in the immunity the immune system (15). Another example is the production by evasion by mycoplasmas. Significance mycoplasmas | immunoglobulin | protease Mycoplasmas are minimal pathogenic bacteria able to infect ycoplasmas are small-sized bacteria belonging to the class humans and a wide range of economically important animals; MMollicutes (1). These organisms are characterized by a fast as such, they are major causes of concern in the medical and evolution that has been marked by a drastic genome reduction, veterinary fields. These pathogens often lead to chronic in- leading to current mycoplasmas having a reduced coding capacity, fections, and their mechanisms of immunity evasion are poorly no cell wall, and a limited number of metabolic pathways (2, 3). As a known. Here we describe a two-protein system from the ru- result, they are obligate parasites and are found in vertebrate animals minant pathogen Mycoplasma mycoides subspecies capri that including mammalian, avian, reptilian, and piscine hosts (4). is involved in the capture and cleavage of antibodies. MIB is Despite their apparent simplicity, many mycoplasmas are path- able to capture the antibodies and to subsequently recruit MIP, ogenic for humans and a wide range of animals, and are major a protease that is able to cleave the antibody heavy chain. The – causes of concern in both the medical and veterinary fields (5). In MIB MIP system appears to be widespread among pathogenic humans, two of the most significant pathogens are Mycoplasma mycoplasmas and is potentially a key player for the virulence pneumoniae and Mycoplasma genitalium, infecting the respiratory and immunity evasion mechanisms of these bacteria. and urogenital tracts, respectively; they are mostly associated with Author contributions: Y.A., S.V., J.J., A.B., and P.S.-P. designed research; Y.A., L.M., C.D.P., diseases characterized by high morbidity and low mortality, like A.L.R., C.E., L.C., and S.C. performed research; Y.A., L.M., C.D.P., A.L.R., C.E., L.C., and S.C. interstitial pneumonia or urethritis (6, 7). In farm animals, myco- analyzed data; and Y.A. and P.S.-P. wrote the paper. plasmas have a high economic impact, thus warranting intensive The authors declare no conflict of interest. veterinary surveillance and regulation. In cattle, one of the diseases This article is a PNAS Direct Submission. listed by the World Organization for Animal Health is the conta- Freely available online through the PNAS open access option. gious bovine pleuropneumonia (CBPP) caused by Mycoplasma 1To whom correspondence should be addressed. Email: [email protected]. mycoides subspecies (subsp.) mycoides. CBPP is still highly preva- This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. lent in Africa, and its mortality rate can reach up to 50% when 1073/pnas.1600546113/-/DCSupplemental. 5406–5411 | PNAS | May 10, 2016 | vol. 113 | no. 19 www.pnas.org/cgi/doi/10.1073/pnas.1600546113 Downloaded by guest on September 25, 2021 M. pneumoniae of the community acquired respiratory distress syn- drome toxin, an ADP ribosylating toxin with vacuolating activity (16). Though some mycoplasma infections can lead to acute in- flammatory episodes, most are chronic, suggesting that these bacteria have developed strategies to face and to evade the sophisticated immune system of mammals (17). The most widespread mechanism involves the antigenic variation of surface proteins, including immu- nodominant lipoproteins. In many cases, the antigens that are subject to variation are associated with cytoadherence (18, 19). Indirect evi- dences also point toward the existence of a molecular mimicry mechanism in M. pneumoniae, because infections by this mycoplasma have been followed in some cases by acute autoimmune diseases (20). It has been suggested that some mycoplasmas can directly target Fig. 1. Genome context of protein M homologs coding sequences. (Upper) the host’s immunoglobulins as a means to evade the immune sys- Schematic diagram of the genomic regions surrounding the genes MG281 in tem. In Ureaplasma, the cleavage of the human IgA1 at the hinge M. genitalium (blue) and MMCAP2_0583 (red) and MMCAP2_0582 (dark region, releasing intact Fab and Fc fragments, has been reported. It green) in M. mycoides subsp. capri. Genes homologous to MMCAP2_0583 are was also shown that isolates of Ureaplasma could cleave the IgA1 of colored in light red, and genes homologous to MMCAP2_0582 are colored in their host species, but not IgA1 of other species (21–23). This ac- light green. (Lower) Schematic representation of the domain architecture of tivity appears to be linked to a serine protease, but the source of this protein M and MMCAP_0583. activity remains cryptic, because no gene candidate could be iden- tified. In the poultry pathogens M. synoviae and M. gallisepticum,a this cluster are expressed